text:
Can civilians buy military aircraft?
Say one wanted to buy a retired F-14, or F-5, or a BAE Hawk. Could I do it?
Obviously this would mean stripping out radars, weapons, rwr, and any other sensitive equipment, but after this, would it be possible?
Is there some kind of procedure for this?
EDIT: What is the typical way aircraft are released for sale? Is it common?

Yes, of course there's a procedure. That's how all those military planes got into all those private aviation museums.

sometimes Courtesy has fancy fighters for sale: http://www.courtesyaircraft.com/index.php/inventory/inventory/warbirds-fighters

Any detailed answer will depend hugely on which country we are discussing. Different countries, different rules.

yes http://www.trade-a-plane.com/for-sale/aircraft/special-use/warbird

Yes and no.
Yes it is possible to buy old military aircraft; they are frequently listed in the pages of aircraft sales periodicals like Controller, Trade-A-Plane, Barnstormers, etc.  Popular piston engine military aircraft include the P-51 Mustang, AT-6 Harvard and T-28 Trojan.  East Bloc jets like the L-39 and MiG-15 are also big sellers, due to their affordability to acquire and maintain.  A number of historical organizations like the Commemerative Air Force operated old WWII fighters and bombers for display and exhibition.  And the unlimited category class at the Reno Air Races is dominated by rebuilt and souped-up WWII fighters like the P-51 and F8F Bearcat.
However it is illegal to buy MILITARIZED aircraft, that is those equipped with weapons, either internal or external, military mission systems eg fire control radars, FLIR/Designators, electronic warfare suites, advanced engines or any other type of equipment or system which have national security classifications or ITAR restrictions associated with them.  Sales of weapons systems like this requires Congressional approval, though, strangely enough, one could argue these restrictions violate the Second Amendment of the Constitution.
The United States has recently clamped down on the sales and imports of military surplus aircraft for this reason.  Nevertheless sales of these products are still occurring.  I recently saw ads for the sale of Panavia Tornado ADV aircraft which the UK is selling off to the highest bidders.  Most likely these birds suffer some sort of demilitarization process.  This usually entails mutilating the airframe to cutout wing hardpoints, removal of the radar and cannon and replacement of these items with counterweights - possibly even restrictions on the engines, stripping out datalink busses and classified avionics LRUs, etc.
UPDATE - One notable case of a civilian trying to acquire a military aircraft that gained national attention involved the Pepsi Bottling Company.  It centered on the following television advertisement for their Pepsi Points promotional campaign.

As it turned out these 'Pepsi Points' could be traded on the open market at the time (as opposed to needing the additional trouble of buying Pepsi products for them) for $0.10/point.  An investor named John Leonard spent 700,000 USD to acquire the required 7,000,000 Pepsi Points, then sent them into PepsiCo and demanded a Harrier in return, claiming that PepsiCo had made an offer in the ad.  PepsiCo refused and Leonard sued.  The judge in Leonard v. PepsiCo ruled that this did not constitute a legitimate offer as required by contract law and that the ad suggested the Harrier simply to be farcical.  Later versions of the ad featured the price of the jet changed to 700,000,000 Pepsi points for added deterrence against future schemes like Leonard's.
Some airframes were destroyed or donated to museums to prevent spare parts from being exported to unfriendly nations; this was the fate of the poor F-14.  All Tomcats which could not be donated as artifacts or for gate guard/pole duty were chopped up and sold for scrap.  The fact that Iran still operates some 70 or so F-14s and concerns about spare parts for the AWG-9 radar sets and AIM-54 missiles ending up there was the primary motivator for this.  Hollywood producer Donald Bellesario attempted to acquire a flyable F-14; the sale was denied.
Still some aircraft make their way through the bureaucratic paperwork and end up in civilian hands.  There is at least one F-16A and one F-18A which are in the hands of private owners and the Tornados discussed above will join those ranks shortly.

Excellent answer, exactly what I was looking for. Any details on the falcon or the hornet?

Lol...That was about 10 years ago, but believe it or not both were actually listed on e-Bay out of all places!  e-Bay also frequently lists MiGs for sale as well.  As for the Tornado ADVs, they're still for sale, if the price is right. (http://www.warbirdsnews.com/warbirds-news/1988-panavia-tornado-adv-sale.html)

"Sales of weapons systems like this requires Congressional approval" You might wish to edit your answer to take into account that the US Congress has jurisdiction over less than 1% of the countries in the world...

@DavidRicherby, Congress has jurisdiction over a far greater percentage of the surplus warbirds, and probably close to a third of new manufacture.

@Mark Sure. But there are a lot of other countries in the world, and a lot of other congresses and it would be nice if answers acknowledged this. Obviously, we can't expect every answer to apply to every country but it would be nice if people said things like "In the US, Congress does X" rather than just "Congress does X."

I'm curious why "advanced engines" would be something to keep out of private hands, given that modern civilian jets have engines just as advanced as those on modern jet fighters and bombers (and often directly derived from same).

Potentially said engines, because of their propulsion use in military aircraft, could be classified under ITAR restrictions as a technology or military export.

You could, if the aircraft is available for sale somewhere, and there are no other legal compliance problems. Paul Allen has a nice collection of military aircraft at his Flying Heritage Collection, and there are certainly quite a few other people with both flyable and unflyable military aircraft. There are also private companies which will let you try out their planes, such as Australian Jet Adventures
Here is a web site which tracks military planes in private ownership around the world:
http://www.warbirdalley.com/

It partially depends on whether the military giving them up are willing to let the technology go. In the case of the F14 every single one had their engines and any novel systems destroyed completely after retirement to keep any parts from getting to Iran, which bought F14s before the revolution deposed the Shah.
As for getting one most militaries go through a middleman of some sort, which one is used depends on the country and branch. There are exceptions for this, for example the UK MOD sells things on-line although aircraft are rarely posted.

I should have been a bit more specific, the military didn't destroy the airframes, but the engines and any instruments and systems that were specific to the aircraft and not available through the open market. So you can't buy a flyable surplus F-14

@DavidRicherby and no doubt most of the ones in museums were donated as a loan with strict limits to what can be done with them in terms of sending them to be shown elsewhere.

@jwenting When I made my comment, the answer was claiming that every last F-14 the US military ever owned had been shredded. Since it no longer claims that, I've deleted my comment.

@jwenting I'm pretty sure that before a museum gets it most of the classified parts are removed. Not much to learn from avionics displays without the chips beneath.

I'm surprised they went to the trouble of specifically destroying the engines, given that the Tomcat's engine of choice, the F110, is a slightly-modified F101, and you can get the good bits of an F101 by stripping down a CFM56, which are ridiculously easy to get ahold of.

Yes, you can!
A MiG-19 was for sale not long ago, also a handmade copy of a Polikárpov I-16, two were build in New Zealand, the first custom-ordered by an Spanish old aviation team, a Russian Space Shuttle, probably never flown, was recently published, the spaceship was offered along with its hangar and a second space flying machine, but becoming aware of these auctions is not easy...


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When is a fuel pump needed on GA aircraft?
When is a fuel pump needed on GA aircraft? I am a flight simmer and have noticed that you can leave the fuel pump off and start/fly the aircraft. When would you use the fuel pump?

Considering it's a SIM, I wouldn't count on it being 100% accurate. Unless, of course, it was developed by Boeing, Airbus, or another manufacturer for actual training of actual pilots.

IVAO, eh? Ah well.... :P

@FreeMan Ftr, many flightgear models do a good job of stimulating fuel and electrical systems.

Refer to the POH for the aircraft but in the PA-28-161 I fly the electric fuel pump is used on take off, landing, and while practicing maneuvers like steep turns and stalls. Most GA planes are configured with either a gravity feed fuel system (like the Cessna 172) or an engine driven fuel pump (Piper Cherokees) that can be supplemented with an electric fuel pump should it quit or become partially inoperative. The FAA has a nice document on it here (see pump feed systems) their opinion is,

The engine-driven fuel pump acts as the primary
  pump. The electric pump can supply fuel should the other fail.
  The electric pump also supplies fuel pressure while starting
  and is used to prevent vapor lock during flight at high altitude.

The switch you see in the cockpit controls the electric pump. As far as I know there is no way to turn off the mechanical pump (not that you would really want to).
The general startup procedure for carbureted PA-28's (low wing mono planes (fuel tank below engine)) often involves turning the fuel pump on, checking for fuel pressure, then turning the pump off. This can also help to prime the lines with fuel, if the lines are dry you will need a few extra cranks of the engine to draw fuel in with the mechanical pump which drains battery power.
Since you claim you can fly with out the pump running we can assume it is an engine pump driven plane however smaller turbine planes that still fall under the GA header may require an electric fuel pump to feed the engine.

In FS I fly the PA34 seneca v(low wing) and a less known light sport tecnam eaglet (high wing) and both have fuel pumps. But thanks very much for the info

The FAA document link is broken

Virtually all GA aircraft, high or low wing, use both an engine driven fuel pump and and electric auxiliary fuel pump.  Typically high wing GA aircraft will use the aux pump only for priming the engine (fuel injected engines) as gravity feed from the main tanks offers a backup in case of EDP failure.  The aux pump is used on low wing aircraft, both for priming the engine as well as a backup in critical phases of flight where EDP failure could be disasterous such as takeoff and landing.  This is due to the low wing arrangement requiring siphon feed from the tanks to the engine.

The carb 172/152's like the 172P do not have an electric pump, especially the older ones. I'm not so sure that the 172P I trained in even had a mechanical pump, here is a similar POH that doesn't show a pump in the feed system at all.

This is true here.

Hmmm, I don't know.  I flew a Cessna 172N a few weeks ago (I'm a real private pilot) and it had a fuel pump switch, which is presumably the electric backup one referred to above.  I have flown the 172N and 172M as well as PA-28 Arrow and Archer and I think they all had fuel pumps?

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Why is there a difference between the procedural track heading and final approach course at Fort Hood (KGRK)?
Looking at the NDB RWY 15 into Fort Hood/Killeen, why is the procedural track from OKEST showing a heading of 151 degrees when the final approach course heading is 150 degrees. Is that simply a typo? The best answer I can come up is that from OKEST to the LOM is 6.3NM on a heading of 151 degrees. Is the 151 heading to GRK VOR or to the LOM using the NDB? Any thoughts?

It's really only confusing because they are within one degree of each other, but this actually happens quite a bit with feeder routes.
The 151 Degree Course NW of STARN
The 151 degree course (and the OKEST intersection) is only used if you are using AGJ as the Initial Approach Fix (IAF). This is the course that you would fly from OKEST towards the GRK VOR (on the GRK 331 degree radial) in order to get to STARN.  After reaching STARN, you would fly the 150 degree bearing outbound from STARN and the rest of the approach using STARN to navigate.
The 150 Degree Bearing NW of STARN
If you were to use STARN as the IAF instead of AGJ, you would fly the procedure turn on the 150 degree bearing from it in order to get yourself established on the correct inbound course to fly the rest of the approach.  In this case, you would never use GRK at all.

As a side note, a 1° shift makes very little difference in a non-precision approach. At 5 miles, 1° corresponds to about 500 feet track offset; at 10 miles, 1,000 feet. You should still always fly the charted procedure, as accurately as possible, but if you get it wrong by 1° nobody is going to notice (and you'll still be well within the protected regions of the approach).

Would it also be depicted like this if we were right at a rounding boundary for magnetic variation?

@falstro No, because the navaid courses/radials are all relative to each other so that wouldn't matter.  In this case though, it's just two different navaids that aren't perfectly aligned.

Ok, makes sense. Thank you for clearing this up!

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What are these numbers visible from the runway at Narita airport?
At Narita Airport on the terminals there are big digital numbers visible from the runway. They aren't in some reliable order- I saw 98,91,93,95,97,99. Maybe they are Aerobridge numbers. I didn't get a photo as I only had my mobile which was off during taxiing. What are they for?

They are big digital numerals only- it was night.

A good way to answer questions like this is to look at the Aerodrome Chart
As newmanth answered, these are gate numbers.

Using Google Maps, you can also see these numbers painted on the taxiway as a guide to taxiing pilots

If you want to understand airport air-side signage, one document I found useful is CAP 637 Visual Aids Handbook. It is a UK CAA document but I expect most of it applies in other parts of the world.
The CAA refer to stand numbers, as far as I know these are the same as gate numbers. They indicate parking positions for aircraft at airport terminals, these are places that allow for the loading and unloading of passengers.
Airliners arriving at airports will know what gate they have to taxi to, and ATC will provide them with taxiway routes. Airports provide signs so that pilots basically know where to find their allocated gate.

Your answer is reasonably good- could you give a little detail in regards to who needs the gate information and how they use the information.

@user2617804 I would say that that would be another question ;)

I'm going to mark back to this answer as its a partial answer.

@user2617804 gate numbers are for people that need to locate the gate -- obviously for pilots that have landed and need to proceed to their assigned parking spot, but also for ground personnel such as baggage handlers (among others).

Without seeing a photo of what you are referring to, I can only guess as to what the numbers were.  Most likely, they were the gate numbers.  At Narita, the gates are numbered odd on one side of the the terminal and even on the opposite.  Here is a diagram of terminal two, which is what you were probably looking at.  At commercial airports, gates are numbered on the outside (in addition to inside the terminal) so that both ground handling staff and pilots know which gate they are at.
Here is a picture of a terminal at Denver International Airport. Note that the gate numbers on on both the passenger loading bridge as well as the exterior wall of the concourse:


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Is there an offline airplane route software similar to the in-flight entertaiment map?
Regarding the software that displays on a video the map with flight information for passengers, I would like to know:
1) The software from various airline companies seems to be more or less of a standard. So they should work in a similar fashion. Which input is needed in order to make it work (i.e., altitude, lat/lon coordinates, temperature)?
2) Is it possible to acquire one version of this software and run it offline as a simulation, giving as input the needed information?
3) Is there a freeware solution to this? I'm more interested on information like the geography, cities, countries and borders.

You want to visualize route of actual past flight? Or filed flight plan? And do you have it as shape (geopoints) or fixes? And what do you need to visualise? Draw a line on a map? Animate icon over map? Or in 3d model? Also which current solutions do you mean? Your question is not really answerable without clarification of those points.

What's wrong with Google Earth?

I've edited the question in order to clarify it. Google Earth can run offline, but you need to access it online first, in order to download the desired maps/regions you want. I would like to avoid this step.

1) The software from various airline companies seems to be more or
  less of a standard. So they should work in a similar fashion. Which
  input is needed in order to make it work (i.e., altitude, lat/lon
  coordinates, temperature)?

"Inputs" from the aircraft devices, like pitot, anemometer, gyro, etc. ? I don't know. DeltaLima answered that for you. What you see on the screen is definately a software rendering, that means an operating system is running, and displays a frame on that screen device. The graphic is software-generated (the map, the plane, its orientation, the text, the sun, the clouds, zooming, etc.)
So, at some point, the inputs signals (altitude, cruise, heading...) has to be converted in computer bytes that will be handled by hardware devices of a computer, buffered in memory, then used by "some software" in the way they have been designed for.
Option 1 :
There's a central Operating System (OS) that holds all the computable datas and feeds all onboard software on demand including FMS, IFE, etc.
analogic device -> convert to computable data (bytes) -> central OS
                                                        / | \
                                                      /   |   \
                                                    /     |     \
                                    Cockpit softwares    IFE    Cabin Softwares

Option 2 :
There's no central OS, but multiples ones, and a direct star-type (tree) data pipeline.
analogic device
 |_ convert to computable data (bytes)
     |_ some software on some OS
     |_ some software on some OS
     |_ IFE softwares on IFE OS
     |_ some software on some OS

Option 3 :
IFE Software is a included in one OS that also run other softwares
analogic device
 |_ convert to computable data (bytes)
     |_ OS1 (cabin)
     |   |_ IFE softwares
     |   |_ Inflight intercom software
     |_ OS2 (cockpit)
     |   |_ Front Panel softwares
     |   |_ BlackBoxes softwares
     |_ HUD software (of packed software in hardware)
      ...
      ...

There are other Options, each one could be better called "onboard System"
By the way, if, by "inputs", you meant "how to make that tiny plane move along the map", there are thousands of ways doing it, but the schemas is the same :

draw a map (use some gree/blue/brown color to make it look good enough)
draw a path using points locations on a X-Y (invisible) grid and line segments
slam a top view of a plane on all of that at a precise X-Y location (and don't forget to rotate the plane icon in the correct heading or your passengers will start to panick)

No matter how beautiful the flightpath could be rendered, remember it's a computer generated graphic, and doesn't need to be accurate at all. For example, refreshing could be set at an interval of 5 seconds instead of real time (5 seconds is good enough even for steep turns on final) The map resolution doesn't require a milimetric precision. 1000ft or 500ft lateral precision could suffice, and even if the displayed (text) altitude is in feet, the 3D rendering doesn't care about that at all : it uses a fraction of that altitude, then accordinly shifts the position of the aircraft model on the screen to give you the impression the aircraft is at an higher altitude...
That the logical way the flightpath software requires. Accuracy and physics computations are not required, unless you want to create a game or even better, a simulator (in terms of reproducing nearly-real behaviour in a virtual world) GoogleEart's Flight game for example isn't as precise as many other games out there (Lock On, X-Plane...)
But for all of those, the "inputs" are all binary datas stored in memory and used as variables by the software. Turning a plane isn't dependent on a heading value. It's one block of the software code that reads the heading variable, then rotate the object (the plane) by the corresponding angular value, then another block of the software code draws (renders) the object on a screen buffer. Finally, the screen buffer is passed to the displaying device (your IFE screen) and each pixel of that screen shows what has been calculated by the software for the human eyes.
In the end, what you see on a screen - ANY screen wether it's your TV, the IFE, your computer screen when you read this answer, your phone screen - is a series of slideshows pictures rendered by the screen device one image after another. But it's done so fast that the human eyes (or brain actually) think what is shown is really moving. It's not, but looks like.

2) Is it possible to acquire one version of this software and run it
  offline as a simulation, giving as input the needed information?

I tend to say yes ! but wait !
Good luck finding that software though. You should ask someone working for an IFE system provider for aircraft manufacturer.
And note one thing : Such softwares could be packed in some hardware components having an inbuilt memory card, this preventing anyone from copying that very software while it is successfully loaded in the IFE OS just like any other software loaded from disk/CDs/USBs... Of course you can't unplug the hardware device from the IFE hardware motherboard, and plug it on your computer motherbord, that wont make it.. Just like your phone (wether android or iphone or whatever) the firmware is burried deep in one hardware component. You can't easily copy a firmware from an iphone to a nexus.. :P
But at one point, those softwares has to be created on a computer, then, have their "saved as files" state in the computers of the enterprises creating them.
As you could have guessed, chances to get a copy of such software is pretty.. non existent, not because it's nearly impossible, but because such software are copyrighted, and/or the (hardware) system supposed to work with aswell. A flightpath IFE software developped by a company may fail to work on your computer if you don't have the same OS architecture as the company's, and/or even some hardware devices that may be required to input or output valid binary datas read/written by the software.
Someone who has a copy of such software wont tell you he has...
I can tell you the Air Austral IFE is Linux based Operating System. The flightpath map displayed, the movies/music/games entertainments are all running on that OS. While the IFE on some Air Madagascar planes could be Linux based aswell, the softwares (the rendering and graphic layout) are different, meaning that those are not the same softwares as the Air Austral ones (or other versions)

3) Is there a freeware solution to this? I'm more interested on
  information like the geography, cities, countries and borders.

An authentic flightpath software like those onboard aircraft ? Nope ! Never seen one in the items library of a store, and never found a page using google of a page "FlightPath Software Download".
A software that shows earth, oceans/lakes, country boundaries maybe ? Yes !

GoogleEarth/GoogleMaps
Nasa Worldwind
Bing Maps
Many little and less widely used software on SourceForge using rendering libraries and web hosted databases
...

A software that allows you to draw/show paths (and objects if possible)

GoogleEarth
Cesium
Nasa WorldWind
Marble
...

A standalone software that shows you (simulated) realtime flight of an aircraft over a map or 3D Earth ?
Anyone who tried creating such software ended making it a web-based application that you can access only through a navigator (like FlightRadar) Otherwise, it would be the decision of an enterprise or organism to hire developpers to produce such software for internal business purposes ONLY !

display aircraft on a radar screen
display meteorogical objects evolution on a map
display satellites movements at a space center on a large screen
(^^ purposes like that that has nothing to do in public domain)

That's exactly what IFE hardwares/softwares is about : have a bunch of engineers/programmers, build the devices/softwares, sell them to airlines/aircraft manufacturers. Panasonic, Thales, LiveTV of JetBlue, Rockwell Collins... Don't expect them to upload their baby on a website and allow you to download them..

So far, I said "anyone who tried..." ... ... failed ! Because building such software, to be accurate enough and interresting for you and me, would require a massive amount of datas :

flightpaths are not straight lines from airport to airport. You can spot this with FlightRadar, then you'll need each airport data, with their SID/STARS; you'll need waypoints, you'll need routes (those you can see on a real jepessen map) etc.
of course, you'll have to maintain those datas up to date.
those datas are NOT freely available, so if you're a developper that paid acquiring them (or a company that employs developpers) you should find a way to make profit on it. That's what Microsoft made with Flight Simulator, what Lockheed Martin is doing with Prepar3d, X-Plane, etc. Games are selling well, but a simple "show my flight plan" software isn't interresting enough to make profit on it. For you or me perhaps, but not at all for average people.
And because the datas has to be updated, a standalone application that doesn't connect to the web would prove impossible to achieve, as it will be obsolete soon enough and would require anyway an internet connexion and mostly a registering (payware) for stream updates. Most applications that does this are web-based applications, not downloadable ! This is even more not standalone if you are thinking of displaying an actual, flying, aircraft (like FlightRadar) - And you'll have to purchase access rights on some radar centers... and implement the programatic logic to handle those streams of datas at runtime.
What about maps ? If the plane is flying above the city of New-York, what are you going to display ? A greenish-brown landscate ? A text showing "New-York" ? What about the shores (or how the software knows there is nearby ocean and land ?) Yes, you must have a landclass/waterclass database. The way the datas are stored highly depends on the way the software displays them. You need raster (images) tiles of the earth if you want photoreal-like terrain, or vector-based datas for computer generated landscapes. The later is lighter in terms of required disk space, but vector-based datas ar good for flat terrains (projections) To have datas for mountains, valleys, etc. you'll need anyway discrete values of land elevation around the globe. The disk space used quickly rockets... So don't expect from someone the task to compile all those datas for you.. and there are awfull voids here and there (in far far away land on this earth) that you can't retrieve freely on the web (well, there are 100 meter resolution terrain elevations available for free out there, but higher resolutions are very hard to get for the entire planet)
That's why on flightplans IFE, you can't zoom in and see roads on the map ;)

I've started developping my own "show aircraft routes and display realtime flying tiny aircraft over a map" years ago, still, it's stucked as a "Work In Progress" due to the massive amount of new issues occuring and the interlacing complex features I would like it to have (Compatible with the game simulators mentionned above)
There's almost one new created airline every week, one new aircraft delivered every day, updating the - offline - database of that program occurs on a daily basis, weekly at longest, and I still need internet for that ! So, the day I may release that application would never come before I die. Just to pick an example, the application is developped as a Windows Forms interface. There's a better interface provided by the dotNet Framework called WPF. Upgrading the application to this new architecture would be a must before releasing it, and I have no time to do that. The database weight several Gigabytes (as expected : Maps and graphics...)

What a great answer! How come you decided to make it CW?

The airshow in several airplanes that I have flown is actually running Windows (I know this because I have seen the blue screen of death on more than one occasion, lol).

@DannyBeckett - Thank you. "CW" ? Sorry, didn't understood. CW vaguely stands for some hardware device to me..

@fsintegral Community wiki... you don't gain rep from it (it can be un-CW'd if it was a mistake).

@Lnafziger - Good to know. The same thing occurs to me onboard an UU/REU B773ER Flight during climb. The cabin turned black 3 seconds, then everyone's IFE went black aswell. Reboot - then the longest loading commandlines I've ever seen in my life with lots of linux-this, linux-that... The BSOD of Windows is horrible, but for once in my life, I just thought windows would have been faster at the moment. :P

@DannyBeckett - aww ! shame on me. "Community Wiki" .. Okay, will remember that :) I made it CW based on an assumption of mine : since I'm not expert, I thought it would be a good thing to let anyone who want to add an usefull info, correct a wrong idea, or improve the answer proposal to do so. I know the thing about reputations, but I'm not really in earning them. Well, that's how I understand the purpose of CW, but I'll check again, could have missed some basic rules, and I'm doing it all wrong.. (Sorry in that case) Thank you for the notification.

@fsintegral No need to stress, that is what it's for :) Personally I'd be inclined not to CW such a detailed answer, but that's up to you! Interesting read!

3) Is there a freeware solution to this? I'm more interested on
  information like the geography, cities, countries and borders.

I don't think you'll find many freeware solutions in commercial aviation, but who knows. If you are interested in geography, cities, countries and borders I wouldn't buy an inflight entertainment system though. That kind of information is freely available on the internet. Google maps or Google Earth would give that info for example.

1) The software from various airline companies seems to be more or
  less of a standard. So they should work in a similar fashion. Which
  input is needed in order to make it work (i.e., altitude, lat/lon
  coordinates, temperature)?

For the route display: departure airport, destination airport, optionally a
number of waypoints. Estimated time of arrival, actual time of departure.
For the current position: latitude, longitude,
altitude and heading.
Also provided: velocity, air temperature, wind speed & heading.

Typically these inputs are provided over multiple ARINC 429 busses from the Flight Management Computer and Air Data Computer, but RS-232 systems exist as well.

2) Is it possible to acquire one version of this software and run it
  offline as a simulation, giving as input the needed information?

I don't think you can buy the software on its own, you'll have to buy the hardware too. That is going to expensive, but you can buy an in-flight entertainment system and provide it with the proper inputs. Quite a big project I think.


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How dangerous can it be if something falls from a flying aircraft?
How dangerous can it be if something falls from a flying aircraft?

"A thorough preflight is performed in order to ensure that all parts will remain flying in close formation for the duration of the planned flight." (I forget who said that first, but I've long since stolen it.)

Anything of notable mass is likely to be very dangerous for anyone on the ground that happens to end up occupying the same point in spacetime...

This is a simple physics problem. Neglecting air resistant, (which in most cases is reasonably safe to do for falling objects), remember that the acceleration due to gravity is -9.81m/s/s! I leave it to you to calculate the speed at which it hits the ground after falling from 10,000 meters! (The sticklers among you may speak of terminal velocity, but I think something like an engine or so wont be affected much by this.)

If you consider bombs as well, very dangerous.

@HCBPshenanigans You absolutely cannot neglect air resistance. It's highly significant and terminal velocity of almost any object is much, much less than the freefall speed would be from 10km in a vacuum. (The latter would be about 450m/s, i.e., 1000mph.)

Last summer one guy was seriously injured near LEAP (Empuriabrava aerodrome) when 1500 litres of water were poured over him. Anything falling from an aircraft IS dangerous.

I dropped a paper E6B out of a 152 when the door popped open once.  It was over a remote forest in Oregon.  The chances of it hitting someone (especially through the canopy of the forest) are so tiny that I never worried about it.

Oh, and air resistance is definitely not something you can ignore... ever... once you get out of high school sophomore physics class.  Especially when dealing with something like a paper E6B computer.  I have to imagine that its terminal velocity is pretty small.

450 m/s which of course is about Mach 1.3. // cc @DavidRicherby

How dangerous?  Very.

@SpongeBob: What's an E6B?

@aCVn: Only at sea-level atmospheric pressure, which, if you're ignoring air resistance...

The standard operating procedures state that before every flight, a thorough pre-flight inspection should be performed. Depending on the aircraft, minute and tiny details are not even omitted.
Things do not normally and occasionally fall off from a flying airplane, the same way as different objects do not fall from a driving car, although the pre-drive inspection of a car is no where nearly as comprehensive as the pre-flight inspection. Yet, how many times we have seen a bumper, guard, muffler or rear-view mirrors falling off?
How dangerous it would be when it happens? This depends on the part which has fallen. Some parts are not noticeable until landing or next inspection and some can cause disasters.
Baltimore Sun reports this:

No deaths or injuries have been reported in such incidents, but the
  Federal Aviation Administration is not even 100 percent certain of
  that.

The proper term for this incident is Things Falling Off Aircraft (TFOA). The pilot must then submit a hazardous material report within 24 hours in case the material can cause further harm.
This site has listed some TFOA incidents:

In August 2000, a KLM Royal Dutch Airlines Boeing 747 was forced to make an emergency landing when some engine pieces plummeted to the
  ground and landed on a crowded Los Angeles beach
On March 10, 2005, a couple taking a stroll through woodlands near Gatwick airport had a lucky escape when a door from a passing British
  Airways jet, crashed to earth. A part of the 70-pound door from a
  Boeing 777 had become dislodged just after take off and missed the
  couple by only 20 feet!
On August 11, 2006, a door fell off from a TAM Fokker 100 from Sao Paulo to Rio de Janeiro. It dropped off 18 minutes after departure but
  the plane was able to return to Sao Paulo without incident. Nobody was
  injured.
An engine exploded on a Japan Airlines flight bound for Tokyo with pieces of the engine falling on a neighborhood in Jakarta. The falling
  debris hurt no one but 16 homes were damaged.
The right wheel of a Blue Panorama Airlines Boeing 737 fell off after it departed from an airport in Spain and was forced to make an
  unscheduled landing amid emergency in Rome.
A similar incident happened near Los Angeles where an American Airlines Boeing 757 lost its right nose gear but managed to land
  safely with 105 passengers on board.
A landing gear door fell off a Delta Airlines Boeing 727 shortly after the plane took off from Boston*s Logan International Airport.
  The 30-pound metal door crashed into an empty street in a quiet
  residential neighborhood.

@Farhan "The right wheel of a Blue Panorama Airlines Boeing 737 fell off after it departed from an airport in Spain and was forced to make an unscheduled landing amid emergency in Rome." The wheel was forced to make an emergency landing in Spain?

Answer - Very dangerous!
I have 1st and 2nd hand information, so I can speak reliably on this issue. In 2005, a NW DC-10 from MSP to HNL noticed abnormal heat (TIT) on #2 Engine on their final approach. The Operations Dept., where I worked at the time, told them that the thrust reverser for #2 had fallen off on the initial climb (approximately 8,000 ft.), and landed in a field adjacent to a public golf course, next to where a lead mechanic lived and he reported it to OP's, as the plane was making their final approach in HNL.
Independently, my 2 sisters were playing a round of golf at that golf course at the time, when one of them looked up in the air, pointing at a large object rapidly falling and said, "What's that?" Later, the following day, I got a good look at 6-7' round, composite metal object weighing about 300-400lbs with a lot of grass embedded into it (how does grass get embedded in the #2 thrust reverser-the engine mounted right below the rudder?) sitting on a pallet on the hangar floor. Needless to say, an object that size and weight falling from that height could REALLY do some serious damage.
But why did it happen?
DC-10's are mostly retired from service now, giving way to much more fuel-efficient airplanes, but it was not common practice to use the #2 thrust reverser, so when 'A' or 'B' checks came around, it was commonly not looked at, as there was 'theoretically' no reason to do so. The card did come up on "C" checks, but the now-deceased NWA had a policy of 'farming out' "C" checks overseas, in which case it was someone in MSP 'verifying' work was done in Honduras, Singapore, China, and elsewhere. Ignore something long enough, especially on a heavy commercial aircraft with lots of vibration and you will reap the consequences! The company immediately inspected all other DC-10's in it's fleet and found several others approaching the shear point that the original one did.
The crew was unaware it had detached in flight; it presented no compromise in the airworthiness(in a normal situation), and it wasn't until it's final approach some 8 1/2 hrs later that they noticed something peculiar, which was verified by OP's. But it could have been a catastrophe on the ground, and it speaks to the fact that there are no shortcuts to safety, no matter how cheap the ticket prices are.
Further information can be found here.

I'm assuming it was verified that the embedded grass wasn't a result of smashing into a golf course lawn at high velocity?

@reirab Couldn't say for sure, maybe some Chinese mechanic pounded in copious amounts of Burmuda grass before he re-attached the thrust reverser-you probably couldn't tell the difference....;>)

I thought the tail-mounted DC-10 engine was #2. #3 would be the right wing engine, would it not?

@FredLarson Absolutely Right-My Bad! The #2 Engine sits directly under the rudder on the tail. Same configuration for the 727-I should know better. Thanks.

@user2479: Not quite the same configuration - on a 727, all three engines are on the tail (the #2 in the middle, pointing straight out the ass end of the plane, with an S-duct; the #1 and #3 on the sides of the empennage).  With the DC-10, the #1 and #3 engines are on the wings - only the #2 engine is on the tail.

@Sean My bad...again. It's been a while since I've seen a 727. I meant to say the #2 was in the center, the same as the DC-10.

A Boeing 757's just been in the news, flight TCX1638 from London Gatwick to Hurghada Egypt.
Shortly after takeoff its emergency escape slide, as well as the unit it was housed in, fell off the jet!

The above photo is of the 4 meter / 13 feet long chute housing that detached. Luckily it landed in a field; I can only imagine the potential for damage it could've had!
Kent Police stated:

The aircraft part that police have been looking for is said to be an overwing emergency slide unit (similar to the one pictured) that is believed to house one of the evacuation chutes that deploy in an emergency after a plane has landed. The uninflated chute is believed to have been trailing from the unit as it fell to the ground.

The AAIB has launched an investigation.

One major issue that must be kept in mind is the sheer lack of probability that something falling from the sky would ever hit somebody.  As a relatable example, it is estimated that over 500 meteorites actually strike the surface of the earth every year, the vast majority of which never hit anyone or anything of value.  The reason is that there is a looooooot of unused space on this planet of ours, space between continents, major cities, even houses inside of said city.  (Also keep in mind that even if a large object hits a house, no matter the origin, that doesn't mean that anyone in the house will be hurt.  Living quarters also have a lot of empty space in them.)
I mean, keep in mind, there have been a lot of cases of entire planes falling out of the sky and for the most part nobody is hurt except (sadly, though inevitably) the people on the plane.  This can even be true when it's near a populated center.  Because there is a lot of empty space even near big cities.
So, yes, I would agree with the other answers that being hit in the head with a piece of junk from an aircraft would be dangerous, probably deadly.  But I would contest that the chances of it actually happening are extraordinarily small.  Not impossibly, but very very small.
Thus, to actually answer your question: I'd say that the vast majority of the time an object falling off of a plane isn't dangerous at all.

Except that, when entire planes fall out of the sky, it's most often close to take-off or landing, which means the plane is near an airport, which means it's over or near a populated area. So quite often people are killed on the ground.

@DavidRicherby I'd love to see some stats on that if you have them.  I tend to read crash reports quite often out of curiosity (even going to the NTSBs database to just check around.)  My gut tells me that the majority of aircraft incidents do not involve ground fatalities.  They do occur, don't get me wrong, but in the vast majority of aircraft accidents, nobody on the ground is hurt.

I only said "quite often".  My impression is also that the majority of incidents don't cause fatalities on the ground. Off the top of my head, the Air France Concorde crash and El Al 1862 both killed people on the ground, near airports.

@DavidRicherby Oh, my apologies, I was in "LSAT Mode" where quite often would be interpreted as "A bit over 50% of the time" as opposed to the more colloquial sense of "it happens more than you might think."  Apologies, I just misunderstood :).

It's true that most plane crashes don't involve victims in the ground, but they involve victims on the ground often enough to be a concern. The same reasoning could be applied to mosquito bites: an overwhelming proportion of mosquito bites don't carry malaria, but the tiny proportion that carry malaria amounts for hundreds of thousands or millions.

@DavidRicherby: And PA103 killed people on the ground despite not crashing near an airport.

Probably not, but it is possible that due to structural failure an engine, vertical stabilizer or the entire plane itself will fall down. Though often the plane will come down shortly after.
It is possible that a small leak lets the waste of the toilet seep out and freeze to the fuselage which can let go and come down in a big chunk.

The Boeing 727 could be damaged itself by that toilet ice breaking loose; it could then be sucked into the port engine. This did happen at least three times

@PeterKämpf: Why specifically the #1 engine, and not ol' #3?

@Sean: The toilet water outlet was ahead of the intake on that side. When ice accumulated there and then suddenly broke off, it could knock a few blades from the engine compressor. The resulting imbalance would overload the engine mounts.

@PeterKämpf: So why didn't they put the toilet drain somewhere other than right in front of an engine intake?

@Sean: Good question. Seems nobody is infallible.

Sample of two engine uncontained failures:

Qantas Flight 32: departing Singapore Nov. 2010
United Airlines Flight 232: over Iowa, July 1989

In both cases, large chunks of rotor discs "went missing". Had they hit someone, it would surely be fatal. Extensive searches were conducted, because they were important in the forensic analysis.

Back in propellor days, airliners would vent waste water from the lavatories on occasion. When jet aircraft began flying at very high (and very cold) altitudes, this could lead to the waste water freezing, and large chunks of ice falling at high speed, so the practice was discontinued.
Many years ago, I recall seeing a photo of a poo-sickle from an airliner that came through the roof of someone's house.


text:
Can you track drones online?
You can tracks planes, automobiles and boats on Internet, but does tracking technology exist for drones and if so, can you follow them online?

No, you can't track automobiles. Waze does not track all automobiles, only those that are using their navigation at that moment. In fact, it tracks whatever uses their navigation, which does not necessarily have to be a car.

Side bar: Yes, @JanHudec, actually you can track automobiles. See: UPS, FedEx and many inter-state trucking companies (in the US, at least). Waze.com, however, will not allow you to track vehicles with very much accuracy unless the trackee hands out a link for the specific trip, then only with the person (s)he gives it to. Waze user/fan - not affiliated w/the company

I think the problem Jan (and I) had with this question is that at first glance it seems the OP is asserting that it is possible to track ALL planes, automobiles and boats. Upon further reading I believe he just means that it is possible to track some p's, a's and b's.

http://www.droneshare.com/ is a site where people can choose to send data about their drone flights, though it currently only shows them after the fact.

https://aprs.fi tracks automobiles, along with lots of other things, but only if the owner is an amateur radio operator with a transmitter installed and powered on.

As far as the tracking on aviation websites goes, no you cannot, at least not with the drones or UAVs available for leisure activities.
In order to track these devices they would either need to be equipped with FLARM or a transponder with Mode-S, which again would require a registration.
Unless you have fitted a GPS transceiver to your UAV which offers online tracking via the vendor's website, you will be unable to track UAVs.
Related:
How do you track and visualize aircraft from home?
Why do helicopters not appear in flight trackers?

Technically it is possible to track large UAVs as well, if they have transponders they would show up like civil aircraft, as in radar trackers.
If they do not have regular ATC transponders, the ADS-B system, which is used for traffic collision avoidance, will give out UAV flight data, which potentially could be published online by anyone with the necessary receiver.
However, small UAVs (smaller than 10kg, let's say) would probably not carry the above mentioned transponders, so possibly their ground control stations sohuld submit flight data to a central server, to allow people following drone flights.


text:
Which trigonometric algorithm does an FMS use to determine distance between waypoints?
When entering waypoints into an FMS, the FMS calculates bearing and distance between them.
Does it use "normal" spherical trigonometry equations, or go for the more accurate Vincenty algorithm which takes the earth to be an oblate spheroid?

Welcome to Aviation.SE. I have to admit I am torn on this one, I am not sure this might be on topic here, but I would wait also for someone else's opinion.

I think it is on topic. I remember seeing spherical trigonometry equations in FMS technical docs, but nothing I have nothing I can refer to.

(I'm no expert) but far from the poles, the difference is too little to play much role. Imprecisions in windspeed are more significant than that. So IMHO, it doesn't matter.

No need for spherical trigonometry when a sphere is concerend. Simple linear algebra is sufficient to determine distance along a great circle route. Less CPU cycles required too. But I have no idea if it's used in an FMS.

Please note there's also a separate problem with terrain-following aircraft when Vincenty isn't enough.

Given that a $50 handheld GPS will use a WGS84 spheroid, and happily convert between alternative spheroids, I'd be disappointed if an expensive FMS used a cruder model.

Does a handheld GPS use more sophisticated algorithms to compute distance between points? Or is the choice of spheroidal model merely for converting satellite-referenced coordinates into a latitude and longitude? Note that if using spherical instead of spheroidal algorithms displaces all the points of the geodesic by about the same amount, the length of the geodesic will change a lot less than the position of either its starting or ending point does.

Which make, model, and version? Ask the manufacturer.

Short answer
Aeronautical data (fixes, waypoints, navaids, instrument procedures) are delivered to aircraft operators and avionics manufacturers referenced to the WGS-84 ellipsoid.
To make is simple the ellipsoid is the volume enclosed by the revolution of an ellipse which best approximates the shape of the Earth, generally in a given region only. WGS ellipsoid is a global one which approximates the whole Earth shape.

FAA provides rules for designing procedures, and algorithms to use to compute various elements, including the distance between two fixes and their relative azimuths. This is described in Order 8260.54 The United States Standard for Area Navigation (RNAV), Appendix 2. TERPS Standard Formulas for Geodetic Calculations:

1.0 Purpose
The ellipsoidal formulas contained in this document must be used in
  determining  RNAV flight path (GPS, RNP, WAAS, LAAS) fixes,
  courses, and distance between fixes. Notes: Algorithms and methods
  are described for calculating geodetic locations (latitudes and
  longitudes) on the World Geodetic System of 1984 (WGS-84)
  ellipsoid, resulting from intersections of geodesic and non-geodesic
  paths. These algorithms utilize existing  distance and azimuth
  calculation methods to compute intersections and tangent points
  needed for area navigation procedure construction. The methods apply
  corrections to  an initial spherical approximation until the error is
  less than the maximum allowable error, as specified by the user.

[...]

3.4 Direct and Inverse Algorithms.
The Direct and Inverse cases utilize formulae from T. Vincenty’s,
  Survey Review XXIII, No. 176, April 1975: Direct and Inverse Solutions
  of Geodesics on the Ellipsoid with Application of Nested Equations.

FMS use ellipsoid geometry to compute distances and angles, in order to match aeronautical data.
A visible consequence is that, except for meridians and equator, prlongating a geodesic on an ellipsoid doesn't draw a closed curve, as if it were a great circle:

Detailed answer: Need for WGS-84
New modes of navigation have emerged with a significantly better accuracy than using VOR-DME and inertial:

RNAV (area navigation) generally uses GNSS (global navigation satellite system, one GNSS being the US GPS),
RNP (required navigation performance),
and more generally performance-based navigation (PBN).

At the same time these new direct modes of navigation (compared to a navaid-to-navaid paths) can define paths extending to thousands of NM, and commonly crossing different geodetic reference systems where latitude, longitude, height and vertical can have significantly different values.
As an illustration, the measure of "height" used to be referenced to local MSL (mean sea level):

(source)
But a GPS receiver, which is now the main instrument to locate a point, can only provide the height above an ellipsoidal simplified Earth model. Latest receivers also provide the height above the simplified sea level model (geoid), but only as the result of a transformation of the ellipsoidal height, etc.

(source)
As visible above, the direction of the local vertical is impacted by the transformation, creating another problem for airborne vehicles navigation.
This can quickly become a nightmare with differences for the same point up to 100m depending on the reference used:
For these reasons, it appeared very early that all elements involved in mapping, navigation and ATC must use the same datum, in all countries. ICAO has selected WGS-84.
ICAO Doc9674:

The Council [...] on 28 February 1994, adopted Amendment 28 to Annex 15,
  introducing the provisions concerning the promulgation of WGS-84-related
  geographical coordinates. [...]

WGS-84 on Wikipedia:

The WGS 84 datum surface is an oblate spheroid (ellipsoid) with major
  (equatorial) radius a = 6378137 m at the equator and flattening f =
  1/298.257223563. The polar semi-minor axis b then equals a times
  (1−f), or 6356752.3142 m.

Current country compliance with ICAO selected datum: See Jeppesen WGS-84 Status Report.
Aeronautical databases
FMS uses aeronautical data (fixes, procedures) in the ARINC 424 format, where legs are WGS-84 paths.

Processing of aeronautical data
I've had difficulty to get the exact authoritative document making mandatory the use of ellipsoid geometry in a FMS, however, from FAA Order 8260.52 related to RNP, FMS are part of the so called GPN means which are referenced to WGS-84:

Geographic Positioning Navigation (GPN).
Navigation based on geodetic
  calculation of geographic position referenced to the WGS-84 ellipsoid.
  Global positioning system (GPS), wide area augentation system  (WAAS),
  local area augmentation system (LAAS), flight management system (FMS),
  RNP, and area navigation (RNAV) are examples of GPN.

When calculating distances between fixes, or angles, a FMS computes geodesics which are shortest paths between fixes. On a sphere this would be a great circle. On an ellipsoid this has to be adjusted, Vincenty's formulas are one of the methods that can be used for approximation.
Additional details on how geodesic calculations are done can be found in FAA Order 8260.58 related to Performance Based Navigation.

If that's the short answer, I am not going to attempt to read the long answer!!!

@FreeMan: LoL. If you read all of the post and don't want the long answer, then the only possibility is to try to clear it from your memory :-) because they are both in the post (but it was not said where one finishes and the other begins). That's a trap I use, because nobody wants to read my long answers.

Actually, I skimmed through, went "ooohhh pretty pictures!" and wrote a snarky comment. Just like I did in calculus class.

The answer is very good for content however more would be better, not exactly a topic that is approachable with short answers.  As tend to happen when involving geodetics and its application via models and processes. But really good to try condense it.

A spectacular answer. Incidentally so is the FAA Order 8260.54 (link included above) - it contains calculators for some of the functions AND detailed algorithms for easy implementation in a programming language.

The requirements for FMS are spelled out in TSO C-115d which further specifies compliance to RTCA DO-283B RNP MOPS.  Para. 1.5.4.1 states; All navigation data is assumed to be referenced to the WGS-84 earth model in accordance with ICAO Annex 15 for lateral and precision landing path points.   And the following paragraph states; The desired path is defined by a series of geodesic tracks joining successive fixes. Appendix E provides an example algorithm for the computation of a geodesic between 2 fixes (aka, the inverse problem of geodesy.)

@Gerry: That's a good addition, this explains why I couldn't find the reference.


text:
Where should I enter the pattern when instructed to report a 2-mile left base?
Say I'm flying heading 275 and am headed in to land on runway 16 at a towered airport in Class D airspace. I'm 8 miles to the east and have been cleared: "report 2 mile left base runway 16". Should I go for a standard 45 degree traffic pattern entry to downwind at midfield or should I fly straight to the base and report when 2 miles east of the runway?
In this case I went straight for the base and reported and didn't get yelled at by the controller but I'm curious what the correct thing to do is in this situation.
I'm not asking what a 2 mile base is, I'm asking where I should enter the pattern if instructed to report on 2 mile base.

possible duplicate of What is a two- or three-mile base exactly?

this is a compound question, "what is a two mile base" and "what to do if told report a base as opposed to enter/join a base".

If you're not sure what the controller wanted, ask!

@egid yeah... my CFI decided to talk instead (not my usual instructor) so I didn't follow up a 19,000 hour guy with a question to ATC. Should have just asked him but didn't really think about it at the time.

I get where you're coming from, but if the guy actually has 19000 hours... he ought to understand a sterile cockpit and shut up for a few while you clarify instructions. :)

Oh, what airport was this at? It sounds an awful lot like Paine Field's (KPAE) phraseology and general habits. :)

KCLL (Easterwood) :-)

I'm assuming you're more interested in the base-or-downwind question rather than the where-is-the-2-mile-base question.
Theoretically you're supposed to fly the published procedure unless told otherwise. In this case the procedure would probably be a standard traffic pattern.
Being told to 'report' means only that, you should report it when you're there.
This is not to be confused with the (in my experience) more common instruction "Enter and report a 2 mile base for runway 16", in which case you head for the base and not the downwind, and you report it when you get there. To argue ad absurdum, the clearance "Cleared touch and go, after the touch and go, make left traffic, report mid-field downwind" doesn't mean you should head straight for the downwind.
As always, when in doubt, ask.

To be clear though - what the controller means is to enter a 2 mile downwind (meaning 2 miles from the runway) and report when turning base?

@Pugz I'd assume he probably said "enter and report", or at least intended to, so I would've asked if he wanted me to go to the base.

Cool thanks! He did not say enter, hence my question.

I too would assume enter was implied, but everyone makes mistakes including controllers.

Curious - I don't see ENTER in the FAA Controller Glossary. Where can I find a better reference of what is meant by this instruction? Do they mean enter the pattern and fly to the base then report or do they mean enter the base directly from your present heading then report?

@Pugz, you might have more luck searching for "entry". "STRAIGHT-IN APPROACH VFR− Entry into the traffic pattern by interception of the extended runway centerline (final approach course) without executing
any other portion of the traffic pattern. (See TRAFFIC PATTERN.)" I'm not sure if there's a similar entry for a base entry, but it's the same logic.

This answer is no longer correct per the P/CG. They now say a "report base" instruction is essentially the same as an "enter base and report" instruction.

You should proceed directly to a left base to Runway 16. Specifically you should aim for a base leg which will set you up to turn a two-mile final.
This is per the Pilot/Controller Glossary term "TRAFFIC PATTERN." In October 2023 the FAA updated the term to include the following notes:

NOTE-
ATC may instruct a pilot to report a “2−mile left base” to Runway 22. This instruction means that the pilot is expected to maneuver their aircraft into a left base leg that will intercept a straight−in final 2 miles from the approach end of Runway 22 and advise ATC.

NOTE-
ATC may instruct a pilot to report “5−mile final” to Runway 22. This instruction means that the pilot should maneuver their aircraft onto a straight−in final and advise ATC when they are five miles from the approach end of Runway 22.


text:
Is there a special way to calculate the (parasitic) drag produced by the propeller?
Is there a special way to calculate the drag produced by the propeller? Can I compute it with the standard formula for parasitic drag, with the circular area of the propeller as the wetted area?
To be more specific. I have a graph of the thrust vs. the incoming speed of my propeller

The prop efficiency is awful. Take a bigger prop and run it at lower speeds.

Not quite. The propeller accelerates air, and the cross section of the accelerated air is slightly smaller than the prop disc area. However, this jet of air will sweep surrounding air with it, so there is no clear boundary. Also, the fuselage or engine nacelle will displace the slip stream / propeller wake, so you need to check what cross section is needed to accommodate both. If you now look at the wetted area in the propeller's wake, you need to calculate two effects:

Increased dynamic pressure and surface speed with fully turbulent boundary layer, causing more friction and pressure drag, and
Propeller swirl, which creates additional lift / side force on the surfaces in the prop wake. Include trim drag to counteract the swirl effects.

Fist you calculate the drag without the propeller, and then with it. The difference is the contribution of the propeller wake. For simplicity, assume a constant speed over the cross section of the propeller wake and do not include the acceleration of surrounding air. For more precision, try to add the deflection of the propeller wake by the wing and consider that the acceleration of the air flowing through the propeller disc is normal to it while the airflow itself comes from a direction described by the angle of attack and the angle of sideslip. If these are not zero relative to the propeller, the propeller wake will have a different direction than the surrounding air flow.
If $\Omega$ is the angular velocity of the propeller, $v_{\infty}$ your flight speed and $\Delta v$ the speed increase due to the propeller of the diameter $d$, your swirl $\omega$ is $$\omega = \frac{2\cdot\Delta v\cdot(v_{\infty} + \frac{\Delta V}{2})}{d^2\cdot\Omega}$$
The speed increase in the propeller propeller wake for a given thrust $T$ is $$\Delta v = \sqrt{v_{\infty}^2 + \frac{4\cdot T}{\pi\cdot d^2\cdot\rho}} - v_{\infty}$$
in air of the density $\rho$. Thrust is engine shaft power times propeller efficiency, divided by flight speed.

This sketch shows the stream tube going through the propeller disc (light grey) and below the pressure profile in the stream tube. Air is sucked into the propeller and pushed out at the back, and the cross section of the stream tube is proportional to the inverse of the flow speed. In the propeller disc, just half of the speed increase $\Delta v$ has occurred (Froude's hypothesis).
EDIT:
This answer by @xxavier lead me to a very interesting paper in which the drag of a Luscombe 8b with and without thrust was compared. A very thoughtful way was used to arrive at zero-thrust numbers, and the result showed that the additional drag from the propeller effects was about 30% of the total zero-lift drag without thrust.

Am I right if you are trying to say that there is no theoretical model that discribes the drag produced by a propeller. I will be more specific: I have a 8"(diameter) x 4" (pitch). It is positioned about 9 inches above my fuselage of my RC Wig. Also I have a graph (Thrust vs. incoming speed) of this propeller, who has a RPM of 8000. (I'll place it in the description of my question)

@SimonRavelingien: The theoretical model is described in my answer. If you hope for a simple equation: This does not exist. The drag will depend on many specifics of your model. In the end you will need to employ the methods of bookkeeping, accounting for every influence and interference by itself.


text:
How is human waste taken care of on commerical aircraft?
Trains, as far as I'm aware, just dump human waste on to their own tracks. There are often warnings like: DO NOT USE the toilet while the train is stopped at the station voiced through the PAs or signed up on the walls. The Daily Mail, in 2014 had an article mentioning: Train companies are to be ordered to adapt their trains to stop dumping sewage on the tracks.
I always kind of assumed that commercial airliners did the same, but I've never heard any warnings about using the restrooms aside from when the seat-belt sign is on.

How do commercial airliners take care of human waste?

At least in my country, also trains don't dump it on the tracks any more. For high speed trains, this would be interesting, especially in a pressure surge when entering a tunnel. All other trains have newer wagons or the wagons got tanks on their last overhaul...

Most trains in the UK store waste as well. Anything built after perhaps the 80s does. The biggest exception is the Mark 3 coaches used by HST (Intercity 125) trains (the diesel trains running up the east coast to Aberdeen and from London to the west from Paddington). These do fling waste out, which at 125 mph can be unpleasant for track-side workers.

I don't think they are the only ones. I frequently see what looks like toilet waste round manchester and intercity 125s don't come up here. I guess some of the older DMUs must be dropping toilet waste on the tracks.

Human waste from the lavatories is collected on-board and later disposed of at the airport after landing.
(Image Source: WikiMedia Commons - Author: Mnts)
Check out this related question here on Aviation.SE:
Where does my pee go when I flush at 35,000 ft?

It should also be noted that although planes do use tanks, there is a phenomenom known as "blue ice". https://en.wikipedia.org/wiki/Blue_ice_(precipitation). You probably don't want that falling on your head.


text:
Practice Pans - are there any genuine reasons not to use them?
I'm a low time PPL.  In my personal opinion, practice pans, perhaps one or two a year, are a good thing.  Practice in a procedure that builds confidence removes one more item from the pucker factor list if it does all go wrong and lets your brain focus on the situation.
The D&D cell are always happy to assist and I know that they welcome it as it gives them practice as much as it does me. They are always excellent and it's comforting to know that they are there if I ever need them for real.
However, I know that many pro pilots do not approve of this.  I am aware that they are often required to monitor guard and that practice pans can be a source of noise but is it really that disturbing?  I've even had that terse "transmitting on guard" broadcast which to me is a) entirely rhetorical and b) great irony.
If something genuine crops up on guard, then of course I'd shut up and continue on my way but are there any genuine reasons for amateurs to not practice?  Surely it's better for all users of the sky to be as good as they can?

I find any transmission on guard, besides sanctioned use by ATC or aircraft in distress, to be moderately distracting and annoying.  Typically someone usually decides the need to broadcast on guard right when I'm receiving pertinent instructions from ATC.  I'm not going to lambast someone on guard, but I am going to simply turn it off--which basically defeats the whole purpose of having guard...

I presume you are from UK since it is the only country I know of that uses practice pans.
Basically, ICAO (ICAO Annex 10, Volume V, § 4.1.3.1.1) states that the emergency frequency 121.5 MHz (sometimes called "guard") shall be used only for genuine emergencies. So typically any other use is considered misuse.
However, countries can file deviations from this rule and publish these deviations in their AIP. One such example is the UK, where 121.5 can be used for practice PAN calls to ensure pilot familiarity with the process.
Pilots not familiar with the situation in the UK sometimes frown upon this use, and as you mention, jump in with the dreaded "transmitting on guard" sentence. But those doing that seem to have the same reaction when a real emergency is going on.
If you are flying in the UK and want to practice an emergency situation you are encouraged to do so by the D&D cells.

The D&D Cell welcomes training fixes and
Practice PANS for controller training on all our
frequencies

But remember to ask permission first:

A/C > London Centre, callsign, request Practice Pan

If they have the time to accommodate you, the reply will be something like

London > callsign, Practice Pan acknowledged, continue when ready

And remember, it is not only a practice for you, but also for controllers. There is a benefit for everyone flying around.
An example of a Practice Pan can be seen in this video

From Get into flying.com

Thanks for the response. I am from the UK and I was not aware that practice pans (or equivalent) are not widespread!  That might explain some of the adverse reactions.  I do indeed always request a practice pan first and have not been refused (I've only done perhaps 4 or 5).  To ward off other comments, I am also aware that the phrase "practice pan" is the only one to be used on guard when practicing procedures.  There is no such thing as a "practice mayday".  Do you happen to know if students and PPLs have any similar procedures in mainland Europe?

One thing that can help those not familiar with the procedure is to let them know that you are intentionally transmitting on guard by appending "on guard" or "transmitting on guard" to the end of all of your transmissions. Then (most) people listening will at least know that it wasn't an accident.

@Simon I don't know of any similar arrangements in other European countries. I'll try and find out.

For the benefit of those of us unfamiliar with UK procedures, what does a Practice Pan consist of exactly? Just a simulated distress call? And if so, who gets to decide on the "emergency" and how far to follow through with the scenario?

It also suggests you might be able to do a practice pan on a frequency other than 121.5


text:
Are there rules governing the conduct of flight attendants?
What are the rules and regulations specified by FAA about the code of conduct of flight crew members?
And, are there any rules which specify behavior of passengers with crew members?

Are you looking for things like "Passengers must obey the instructions of aircraft crew"?

Or a rule specifying that flight attendants must be polite? Because I don't think that exists.

Not really polite, but something like code of conduct for crew members.

The FAA is responsible for safety regulations and standards, not for code of conducts or courtesy regulations for interactions between flight attendants and passengers. Flight attendants are bound to certain behaviour only by their employer and their code of conduct, additionally to any national law that prohibits insulting others or harming them otherwise.

Flight crew members are bound by the rules as specified by the airlines. Additionally, pilots are bound by the rules decided by the Air Lines Pilots' Association, International. These are called code of ethics, and you can have a look at them here


text:
Are there any aircraft where wing, horizontal empennage and optionally canards produce positive lift?
Planes are more stable if the center of mass is ahead of the center of lift. But this means that the tail must provide downforce to keep the nose up, which is inefficient.
Are there any designs where all horizontal surfaces support the craft in the air? The three-surface craft wiki article makes it unclear whether all three surfaces provide upward lift.
In terms of stability, there are several ways this could be maintained. One is to enlarge the rear stabilizer and/or adding wingtips on the rear-most wing. Both of these would weathercock to reverse yaw. In terms of pitch, the nonlinear angle-of-attack-lift coefficient relationship could potentially be used to keep pitch stable. Another possibility is an active control systems, which is used in some fighter jets and birds (more unstable means more maneuverable).
Edit: Birds gain extra lift from their tails.

Are there any designs where all horizontal surfaces support the craft
in the air?

Absolutely.
Canards, as per the designs of Burt Rutan, for one.  Not to mention the Wright brothers!
Also, many "free-flight" model airplanes (which operate with no pilot guidance of any kind) have been designed with lifting tails (horizontal stabilizers), with tail airfoils with a concave top surface, and the bottom surface more or less flat. Models of this nature have been flown regularly from the 1930's or the 1940's, up to the present day. In these designs, the horizontal tails typically are rather large.
Re the free-flight model airplanes, it has been argued that the prevalence of these designs is an artifact of certain provisions in the contest rules (e.g. the model is limited in wing area, but tail area is not counted), and that a neutrally-lifting or down-lifting (and also smaller?) horizontal tail would actually be more efficient, but nonetheless these designs do exist.
Furthermore, evidence exists that even in many general aviation aircraft such as the Cessna 172, the horizontal tail provides upward lift in cruising flight when the aircraft is operated near the aft edge of the allowable CG envelope.1
Last but not least, consider tandem-wing aircraft designs, many examples of which may be seen here.
(As an aside-- soaring hawks typically spread their tail to the maximum possible extent when circling in thermal updrafts, to maximize lifting area.  In many cases the wings are visibly swept forward, which would help balance the uplift from the tail.  It appears that the anatomy is such that sweeping the wing forward also increases wing camber, and thus lift coefficient.  When  gliding between thermals--when the optimum airspeed in still air would be the speed that maximizes the L/D and Cl/Cd ratios, and the optimum airspeed against a headwind would be higher than that--the tail is typically folded, and the wings are no longer swept forward. The faster the bird wants to fly in the glide, the more the wings will be folded (by sweeping back) to optimize the glide ratio for that particular airspeed.  In the simple case of an aircraft of fixed shape, the optimum speed for minimizing the sink rate, and thus for maximizing the climb rate in a thermal updraft, is the speed that optimizes (Cl ^3 ) / (Cd ^2) -- this will be significantly slower than the speed for max L/D ratio (which is also the speed for max ratio of Cl / Cd). So you want to fly slower when circling in a thermal than when gliding between thermals-- and even more so if you have the added advantage of variable-area (foldable) wings and tail.)
Footnotes:

See this section of John Denker's excellent "See How It Flies" website.  Scroll down to the sentence beginning "Here’s an explicit example. I’ve actually done the following experiment:"

Someone could google up some suitable images of free-flight model airplanes showing the conformation I'm describing-- I don't have time to do it right now but might make an addition a bit later--

I don't buy that article about the 172 where he validates his theory looking at tufts on tail tips.  To be in trim with the tail making up lift, the net pitching moment from the main wing has to be nose up to provide a counter force for the tail to work with to balance at given AOA.  The CG would have to be much farter aft, probably aft of the NP and the airplane would be quite unpleasant to fly. To work, you would have to make the tail much larger and shrink the main wing to move the NP aft of the CG, and voila! you now have a tandem wing a/c, like a Q2 or Flea.

Nose-up pitch with velocity increase is not incompatible with positive lift by a conventional stabilizer.  All that's actually required is that the forward surface must always have a higher coefficient than the after surface; this is the same for canards, tandems, three-surface aircraft, and conventionals with either positive or negative lift at the tail.

@ZeissIkon but you don't actually see that with conventional a/c.Main surface net pitching moment is always ND, to one degree or another, and the tail has to produce a NU pitching moment to balance it to be able to trim the main wing to a given AOA. Therefore its lift has to be downward FOR TRIM (not static stability). If the tail is lifting for trim, the net pitching moment forward has to be NU. This only occurs with canards and tandems.  The entire point of tandems and canards is elimination of drag losses from the stabilizing surface having to work against the main surface to trim to an AOA

Yes, there are designs using forward canards, for example the Rutan VariEze, Long-EZ and Beechcraft Starship are excellent examples.  There is also the Eurofighter Typhoon.

But perhaps the best example is the first powered airplane, the Wright Flyer, which used a forward canard.

All that's required for any layout -- convention, canard, or three-surface -- to fly with static stability is that the more forward surface(s) must fly at a higher coefficient of lift than the rearward, so that any increase in speed produces a nose-up moment, or a decrease produces nose-down.
With canards, all I've seen fly with positive lift on the canard stabilizer.  As noted in another answer, it's also been relatively common for free-flight model airplanes intended for competition to glide with positive lift on the (conventional layout) stabilizer (free-flight competition often involves a relatively short power run followed by an optimized glide).
For a three-surface layout, it would be less common for the rearmost surface and canard to both operate in positive lift -- if the center of mass is rearward enough to fly the rear stabilizer as a lifting surface, the front might need to be in negative lift, and vice versa -- but there's nothing that would prevent careful weight trimming from allowing this.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the straight-and-level altitude record for a heavier-than-air winged/lifting-body aircraft?
There are many variants of the flight altitude record. The highest on the list is SpaceShipOne but rocketry isn't really "flight" in the sense of aerodynamic lift. What is the highest altitude for which:

The flight at a reasonably constant speed and altitude "straight and level". It is not in free-fall, so the "cabin" feels about 1g.

It is "heavier-than-air" and supported by lift rather than buoyancy. The engine thrust's vertical component is much less than the weight of the aircraft, so the wings or lifting body have to support the craft.

The speed is slow enough that centrifugal effects are negligible (i.e. it is not in orbit). This is the case below about 2.5 km/s (about mach 8).

The highest on the list that may qualify is in a Mikoyan-Gurevich MiG-25 at about 36000 meters. However, it is not clear if this was at the top of a parabolic arc initiated at a lower altitude. The highest (including unmanned) that surely fulfills the above requirements is the Helios HP01 at almost 30000 meters. Edit: this number isn't reliable or believable.
Helios HP01, although very light, is a very low-power craft that only uses propellers. One would think (sc)ramjet-powered craft would win due to the high speeds needed to generate lift in such extremely rarefied air. Is this the case?

Ymb1 mentioned the highest verified horizontal flights. Adding to their answer however, the following planes reportedly went higher:

Brian Carroll said he flew an English Electric Lightning to 87,300 ft (26.6 km) MSL. From his description it seems it wasn't a zoom climb but an aerodynamic/horizontal flight:

"I once had an F-53 Lightning up to 87,300 feet over Saudi and it was really on a knife edge. Both engines remained alight, but were very touchy, and getting down to a more reasonable and sane altitude needed delicate handling. Earth curvature was visible and the sky was quite dark." Source

The unmanned solar-driven propeller plane AeroVironment/NASA Helios reportedly achieved a peak altitude of 96,863 ft (29,523 m) MSL and spent more than 40 minutes above 96,000 feet. Since the Helios didn't shoot any images at its alleged peak altitude and having a maximum speed of 23.5 kts, these altitudes sound unbelievable, especially for a propeller plane.

The unmanned scramjet NASA X-43A is said to have flown around 110,000 ft (33.5 km) MSL at almost Mach 10. Hence those would be the current horizontal altitude and airspeed records for a non-rocket airplane.

@quietflyer I didn't either.

23.5 indicated is over 400 true at 96000 feet.  A "propeller plane" (helicopter) is currently flying on Mars.

@RobertDiGiovanni I don't know whether they mention true or indicated airspeed. But the maximum speed, I guess they would mention the one near sea level if it would really be over 400 kts. I think the altitudes could have been a wrong instrument reading and the Helios actually reached around 66,000 ft similar to the NASA Pathfinder (would still become an electric-powered propeller plane record). Ingenuity is no propeller plane, it's a helicopter. Mars' CO2 atmosphere is denser and the planet has a 62% lower gravity. I would have added Ingenuity to the answer but OP clearly asks on planes.

One may hope RADAR works a bit better these days, but you are right about weight savings (wing loading) being important for absolute ceiling (level flight).  With sufficient power, fast props may work as well as fast wings.

Sea level at 23.5kts is almost the same lift and drag force as 400 true kts at ~30000 meters. However, 30000m requires about 20 times the power and is almost transonic. That sounds very hard for solar panels and batteries.

As far as one can trust NASA to be a reputable source, an A-12 registration 60-6932 operated by CIA flew at 90000ft on 14 August 1965.
There are unofficial accounts that the altitude record of A-12 is actually 94000ft (by A-12 and later SR-71 pilot Ken Collins), but I was unable to verify this. I am inclined to believe this may very well be true, as the 90k is a bit too round and nice of a number, and many of the documents concerning A-12 are still classified or even destroyed, as the Oxcart program was a very sensitive subject in its own time. It was deliberately intensely hushed out as the airforce variant SR-71 took over in late 60's, and as a less secretive and not as "politically incorrect" technological marvel, the "family model" was a perfect posterboy for intelligence supremacy of the U.S. It did not, however, match the performance of the smaller and lighter A-12.
Click here to download the NASA document containing information on the altitude records of the blackbirds (and more).

That's an interesting answer and pdf. Some did say the A-12 flew to 90,000 ft while Wikipedia mentioned a lower altitude record than the Blackbird's.


text:
How did the nose landing gear of JetBlue Flight 292 get stuck sideways?
The nose landing gear of the Airbus A320-200 was jammed, but the tires were perpendicular to the fuselage. How did that happen?

Slightly off topic, but serious kudos to the pilots for a picture (video) perfect landing - straight down the center line! There was surprisingly little damage to the plane, though I'm sure the nose gear got a thorough going over.

According to the complete NTSB report, following is a summary of what had caused the nose landing gear (NLG) to rotate 90° on Flight 292.

During flight, Brake Steering Control Unit (BSCU) performs1
  cyclic tests which slightly rotates NLG from the 0° position. Due to
  this fatigue, two of the four anti-rotation lugs on the NLG upper
  support assembly fractured and separated. This allowed NLG to deviate
  from the 0° position. Another contributing factor was BSCU system
  logic, which prevented NLG from centering. Also contributing was the
  lack of a procedure to attempt to reset the BSCU system under these
  conditions.

This website has some nice pictures of nose landing gear before and after the landing.
A summary of the investigation can be found here.

1: BSCU has other functions too.


text:
Can the "G" and "VRB" wind conditions be combined in METARs?
I have never seen the "VRB" (for wind direction variations < 60°; e.g. VRB12003KT) and "G" annotation (for gusts > 10KT wind speed difference; e.g. 12003GT30KT) being combined in a METAR.
Until now I have just seen:

VRB03KT (so "VRB" without gusts)
12003G30KT 090V150 (so "G" with wind direction variation > 60°)

Why does this never happen? Is there a rule and is it not possible or does it just never happen?

But why does it not make sense?

@Cyb3rKo, because VRB means there is no recognizable prevailing wind direction at all and so the letters VRB replace the direction. If there is a prevailing direction, the 12003KT 090V150 form is used.

@JanHudec Oh yeah, you're right, silly mistake... I corrected it.

Yes, it is possible for a METAR to contain both VRB and G. VRB10G25KT is valid.
The reason it rarely happens is because, as wind speed increases, major variations in wind directions tend to disappear.

Ok, thanks for your answer!

As other answers say, yes, this is valid. It appears approximately 150K times in our database of 85 million METARs[1]. This database is built from data provided by NOAA and covers roughly 16 months.[2]
Here are several real examples from February 2019.
KBML 011110Z AUTO VRB06G18KT 7SM OVC029 M16/M22 A3007 RMK AO2 T11611217
KSZY 011115Z AUTO VRB06G11KT 10SM FEW050 BKN070 OVC110 08/M04 A3020 RMK A01
ENST 011120Z VRB13G28KT CAVOK M02/M11 Q1011 RMK WIND 300FT 11027G39KT
LFBH 011130Z AUTO 16009KT 9999 FEW042 OVC068 07/05 Q0985 TEMPO VRB15G30KT 3000 SHRA BKN020CB
LFRS 011130Z AUTO 20009KT 9999 FEW016 BKN200 07/05 Q0983 TEMPO VRB15G25KT 2000 TSRA BKN010 BKN018CB

85% of METARs containing this pattern are marked as AUTO. 11% of the time the pattern occurs after TEMPO, though it could also occur elsewhere in the METAR.
I did a quick, simple pattern match to obtain these numbers so they are approximate.
[1] - This database is part of the VOCUS product suite. I work for the company that makes VOCUS. We use weather data to analyze risk prior to flight, and to provide post flight analysis.
[2] - I have an archive of an additional 201 million older METARs if anyone is really interested in numbers against a larger data set.

Oh ok, interesting... So the chance is at approximately 0.2%. I appreciate your research, can everybody gain access to those databases or do you have because you work on VOCUS?

@Cyb3rKo The source data is public. Various organizations provide it, usually in the form of a file/list containing the current/upcoming METARs/TAFs/NOTAMs/etc for an airfield. Having historical data available to query like I did is more unique.

Great answer, and thanks so much for identifying your data source and affiliation.

To elaborate on a previous answer, large changes in wind direction on short timescales tend to be caused by thermal updrafts passing through the area, tending to "suck" the wind toward their centers.
When the overall windspeed is high, the (relatively) small changes in wind velocity (speed and direction) caused by this phenomenon tend to be dwarfed by the overall prevailing wind.
In addition, strong wind tends to suppress thermal convection, at least near the ground.
On a windy day, there still can be some significant changes in wind speed, caused by turbulent "rotors" (tumbling masses of air) intermittently mixing the stronger wind aloft down to the surface, but these tend not to involve extreme changes in wind direction. This intermittent turbulent mixing will be more pronounced on a sunny day (or with an unstable airmass) than on a cloudy day (or with a stable airmass).
It is useful to know that even on a windy day, there can be some significant change in wind direction as the turbulent "rotors" make the wind speed increase and decrease, and it typically happens in a systematic way-- due to a phenomenon called the Eckman spiral, the wind aloft tends to be more westerly (in the northern hemisphere, and more southerly in the southern hemisphere) than the wind at the surface.  So as the wind gusts up to a stronger value, it typically "veers" in the direction that is aligned with the wind higher up.  This is good to know if you are a pilot-- and is absolutely essential to know if you are a racing sailor.
Similarly, as your aircraft rises up through the air after take-off, it will typically (in the northern hemisphere) tend to "feel" a temporary increase in apparent wind from the right (or a temporary decrease in apparent wind from the left), which may have some noticeable affect on handling.  And the reverse on landing.  And all the reverse in the southern hemisphere.  And all disappearing or being greatly reduced near the equator.  Since these effects are dependent on a marked change in wind direction with altitude, they tend to be more pronounced on a cloudy day or with a stable airmass, and less pronounced on a sunny day or with an unstable airmass, when the airmass tends to be more "churned up" by turbulent mixing.

Thanks for this absolutely detailed answer. So the chance that you can find the case of "VRB" and gusts being combined is very low?

I would tend to think so, but haven't perused the METARS to any great extent.  Somewhere in the desert where the thermal convection is really really strong, in the middle of the afternoon on a day when the overall prevailing wind is light, seems to be the best prospect for that to happen.

As Tim Medora found out: the chance of this combination to appear is at approximately 0.2%.

It is possible as @tim-medora indicated in his answer.  Part of the reason this is possible is in the timeframe which each part of the wind information is gathered.  Wind direction and speed is averaged over two minutes while gusts are the maximum gust over the previous ten minutes.
Office of the Federal Meteorological Handbook - Surface Weather Observations and Reports

Wind Direction.
The wind direction shall be determined by averaging the direction over a 2-minute period. When the wind direction sensor(s) is out of service, at designated stations, the direction may be estimated by observing the wind cone or tee, movement of twigs, leaves, smoke, etc., or by facing into the wind in an unsheltered area.

Variable Wind Direction
The wind direction may be considered variable if, during the 2-minute evaluation period, the wind speed is 6 knots or less. Also, the wind direction shall be considered variable if, during the 2-minute evaluation period, it varies by 60 degrees or more when the average wind speed is greater than 6 knots.

Wind Speed
The wind speed shall be determined by averaging the speed over a 2-minute period. At
designated stations, Table 5-1 shall be used to estimate wind speeds when instruments are out of service or the wind speed is below the starting speed of the anemometer in use.

Wind Gust and Squall
The wind speed data for the most recent 10 minutes shall be examined to evaluate the
occurrence of gusts or squalls. Gusts are indicated by rapid fluctuations in wind speed with a variation of 10 knots or more between peaks and lulls. Squalls are indicated by a sudden onset of wind where the speed increases by at least 16 knots and is sustained at 22 knots or more for at least a minute. The speed of a gust or a squall shall be the maximum instantaneous wind speed.


text:
Is takeoff permitted from an aerodrome inside a CTR when it's outside the tower's operating hours?
I am departing from an airfield which is within the CTR of a nearby airport but outside tower operating hours. The chart doesn't specify this situation.
According to ICAO rules,
Am I allowed to take off or not?
EDIT: this is not an EASA or FAA specific question. Rather international, ICAO rules, but if there are different conventions it's also good to know.

It would be helpful if you would add EASA tags, and/or mention the country in plain language.

Yes, but my question is not EASA nor FAA specific.

Well, the answers might be though...  You specified LESL, which when I looked it up is in Spain.  But I see you have since deleted it.  Really, valid answers will depend on the airspace classification and rules for the country you are in.  I don't think there is a single answer that will cover every scenario, and your question was probably better before with a specific example.

Also, VFR or IFR?

VFR of course. My expectation is that class D will revert to E or G as stated in your answer, but it's more general in the sense of. What if it's not specified in the chart? Can an airspace class D exists without ATC at time?

I'm not sure what you are asking...  What if what is not specified in the chart?  If Class D exists it would be depicted, if it is not depicted there is no Class D.  Right?

I don't mean in case the class D is not specified. I mean if what happens outside the ATS hours is not specified.

I think the question is clear. If the answer is "nobody knows", fine, but I don't think there is an issue with this question.

Re "Yes, but my question is not EASA nor FAA specific."-- I don't think that's true.  For example, I don't think the question is meaningful at all in the context of the US.  I don't think the phrase "aerodrome inside of a CTR" has any meaning in that context.  Of course, I may be wrong-- but I would hope the question would have some content that would educate me on the error of my ways if that were the case.  Anyway I live in the US and have no idea what a "CTR" is.

Re "VFR of course. My expectation is that class D will revert to E or G as stated in your answer, but it's more general in the sense of. What if it's not specified in the chart? Can an airspace class D exists without ATC at time? –" -- in the US, it's never specified on the chart what the airspace reverts to when the tower is closed.  (Except in the cases where there is an "extension" adjoining.)  You have to check the Chart Supplement.

But I'm sure that in the US, it is never intended that the airspace remains Class D when the tower is closed.

Different countries have different ways of dealing with what happens with airspace outside ATS operating hours. It is impossible to answer this question without you specifying a jurisdiction

@quietflyer: "I live in the US and have no idea what a "CTR" is". in the ICAO wording CTR is a controlled traffic region, generally below a TMA, managing arrivals and departures to/from an airfield. Used in most countries, in Europe but not limited to. For FAA it should be a class D airspace managed by a TRACON.

@expeditedescent What's the ICAO standard? Normally if an ICAO member doesn't respect it, should publish a difference. I am more interested in the rule, not the exceptions.

@quietflyer I am surprised to learn there are no CTRs in the US. I flew in Europe and America and there were CTRs everywhere, but I never flew in the US.

@Gus The FAA has a way of doing everything differently from the rest of the world :)

If this question were edited to say "According to ICAO rules" at the front, would it answerable?  I'm not knowledgable about ICAO rules to know if that would make sense, but I hate to see to this question be closed.  Yes you could argue that that would invalidate an existing answer but in this case perhaps the answer should not have been offered yet if the question clearly needed some work.  Anyway I'd suggest you make that edit Gus and then I suspect people will vote to re-open.

(I mean, you already did, w/ the last sentence, and looks like people are already voting to reopen, but you could put it at the front for more clarity.)

Done, if you manage to re-open I will accept answers. Even stuff like "It's not really specified." or "It should be written in the chart, If it's not nobody knows".

In the United States, if you are VFR at an airport in Class G or E airspace, you may take off without needing clearance or permission from ATC.
Normally Class D airspace reverts to E or G outside of tower operating hours, therefore no communication with tower is required or even possible.